Fishermen have long known that many species of fish congregate seasonally in areas of pronounced topographic changes in the sea bottom. These areas tend to concentrate particulate matter which enhance microbial (bacterial) growth and promote the propagation of other elements within the food chain. This environment, along with the natural shelter provided by the physical relief of bottom features, is the basis for fish attraction to the structure.
Artificial reefs are submerged structures designed to mimic the habitat provided by natural reefs. They are generally designed for the purpose of enhancing fishery resources or commercial or recreational opportunities, and in the remediation, mitigation or enhancement of adversely impacted marine ecosystems. The artificial reef enhancement causes fish aggregation and increased fish population (including spawning) in areas which are virtually devoid of either reef or pelagic species.
The first artificial reefs were actually shipwrecks and were noted to be extremely effective in attracting fish. Large artificial reef construction efforts involve the disposal of old ships and oil drilling structures, the disposal of used tires and the deposition of coal combustion waste products.
Waste materials such as coal slag and stabilized fly ash have been proposed as reef materials. The need to dispose of these waste products and the limitation of existing landfill capacity appear to be the driving force behind this effort.
Automobile tires and concrete shapes are now the most commonly used products for artificial reef systems because of their availability. Automobile bodies and appliances have also been used extensively. The use of tires is reportedly no longer permissible by United States regulatory agencies, and car bodies or appliances are discouraged because of their tendency to rust away rapidly.
Concrete and stone provide suitable materials for artificial reef construction because of their density, durability and low cost. However, heavy equipment requirements for deployment and costs of transportation have greatly limited the application of these materials.
A current approach to reef design is to create those aspects of natural reefs which are important to desired fauna. This differs from the earlier methodology of using scrap materials or rocks to recreate only the structure of natural reefs. Many of the newer reef units are fabricated from reinforced or prestressed concrete, steel, fiberglass or a variety of composite materials. These artificial reefs offer a number of advantages over either scrap material or rock reefs. The flexibility inherent in a design structure permits the fabrication of modules which are stable, permanent and effective for the reef objectives. Examples of some artificial reefs follow.
Van Doren U.S. Pat. No. 4,997,311 is directed to an artificial reef construction employing a dome-shaped, thin-walled enclosure of plastic material having apertures to permit aquatic life to enter and exit.
Laier et al. U.S. Pat. No. 4,947,791 is directed to an artificial reef consisting of a system of flexible, buoyant geometric bodies, each being formed of a plastic material and having a large plurality of holes or openings. The bodies are anchored to the ocean floor and allowed to float, via a tether line, above the ocean floor.
Rambo U.S. Pat. No. 4,840,516 is directed to an artificial reef formed of a plurality of connected adjacent blocks assembled in side-by-side relation, with each block alternately having downwardly extending trapezoidal, prismatic projections.
Kimura U.S. Pat. No. 4,316,431 is directed to an artificial reef constructed with square bar materials and plate materials. The plate materials are ultimately piled on the bar materials in a manner to provide open spaces for shelter.
Baass U.S. Pat. No. 4,334,499 is directed to an artificial reef system having a base portion formed by a discarded tire partially filled with concrete. A plurality of strands of wire rope extend through apertures formed in the upper side wall of the tire. These strands are allowed to sway in the ocean current to mimic a flora environment.
Kikuzawa et al. U.S. Pat. No. 4,465,399 is directed to an artificial reef system comprising a plurality of hollow cylindrical structures attached together.
Rauch U.S. Patent No. 4,818,141, Creter, Jr. et al. U.S. Pat. No. 4,913,595, and Scott et al. U.S. Pat. No. 4,790,685 are all directed to shoreline breakwater systems to prevent shoreline erosion. While not technically artificial reefs, the systems include base modules placed adjacent to the shoreline in a sloping fashion to deflect and slow down the incoming waves.
One major problem with many reef materials is that the development of the primary film of microorganism, necessary for the establishment of a suitable aquaculture community, is inhibited. Many plastics, metals and other materials contain toxins which prevent the growth of the initial film of microorganisms in much the same way as anti-fouling paint inhibits biofouling. Some materials, such as metals, slough off over time, thereby removing the coating of biofouling organisms. Without the establishment of a permanent biofouling community, a true reef is never formed.
One solution to the problem associated with artificial reef structures is disclosed in the inventors' own U.S. Pat. No. 4,913,094, which is incorporated herein by reference in its entirety. U.S. Pat. No. 4,913,094 discloses a system of artificial reef modules intended to be positioned on the floor of a body of water for creating a feeding and shelter environment for fish. The module includes a column of corrugated sheets formed of polyvinyl chloride (PVC), each sheet having a predetermined surface area for allowing the attachment and growth of microorganisms. The sheets are attached together along their length so that a plurality of partially enclosed spaces are created to act as shelter for small fish from their predators.